The present invention is related to a process for making a work piece having a major phase of xcex1xe2x80x3 from a titanium alloy, and in particular a process for making a biocompatible low modulus high strength titanium-based medical implant having a major phase of xcex1xe2x80x3.
Titanium and titanium alloys have been popularly used in many medical applications due to their light weight, excellent mechanical performance and corrosion resistance. The relatively low strength commercially pure titanium (c.p. Ti) is currently used as dental implant, crown and bridge, as well as denture framework. With a much higher strength than c.p. Ti, Ti-6Al-4V alloy has been widely used in a variety of stress-bearing orthopedic applications, such as hip prosthesis and artificial knee joint. Moreover, the lower elastic modulus allows the titanium alloy to more closely approximate the stiffness of bone for use in orthopedic devices compared to alternative stainless steel and cobalt-chrome alloys in orthopedic implants. Thus, devices formed from the titanium alloy produce less bone stress shielding and consequently interfere less with bone viability.
Various attempts at providing low modulus, high strength titanium alloys for making medical implants with less stress shielding have been proffered by the prior art. There is still a great interest in finding a lower modulus and higher strength titanium alloys. In addition, studies have reported that the release of Al and V ions from the medical implants might cause some long-term health problems, for example the low wear resistance of Ti-6Al-4V alloy could accelerate the release of such harmful ions. Therefore, a primary objective of the present invention is to provide a process for making a work piece, and in particular a biocompatible low modulus high strength medical implant, from a titanium alloy free from potential harmful components.
The present invention provides a process for making a work piece having a major phase of xcex1xe2x80x3 from a titanium alloy comprising the following steps:
quenching a work piece having a temperature higher than 800xc2x0 C. to a temperature lower than 500xc2x0 C. at a cooling rate greater than 10xc2x0 C./second between 800-500xc2x0 C., so that the cooled work piece contains xcex1xe2x80x3 phase as a major phase, wherein said work piece is made of a titanium alloy selected from the group consisting from the following a), and b):
a) a titanium-molybdenum (Tixe2x80x94Mo) alloy consisting essentially of 6-9 wt % of Mo, and the balance titanium;
b) a titanium-niobium (Tixe2x80x94Nb) alloy consisting essentially of 10-30 wt % of Nb, and the balance titanium.
Preferably, said cooling rate is greater than 20xc2x0 C.
Preferably, said quenching comprises water quenching.
Preferably, said work piece has a temperature of 800-1200xc2x0 C. before said quenching.
Preferably, the process of the present invention further comprises casting said titanium alloy to form said work piece having a temperature higher than 800xc2x0 C. prior to said quenching.
Preferably, 6. the process of the present invention further comprises metal working said titanium alloy, and heating the resulting work piece to form said work piece having a temperature higher than 800xc2x0 C. prior to said quenching.
Preferably, said titanium alloy further comprises one or more incidental impurities selected from the group consisting of carbon, oxygen and nitrogen, wherein a total amount of said one or more incidental impurities is less than 1 wt %.
Preferably, said work piece having a major phase of xcex1xe2x80x3 is a medical implant.
Preferably, said titanium alloy is a).
Preferably, said titanium alloy is b), and more preferably said titanium alloy contains 13-28 wt % of niobium.